Mitsubishi Motors Corp's top two executives are likely to resign over the Japanese automaker's manipulation of fuel economy data, Japanese media reported on Wednesday, in a scandal that has halved the company's market value in a week.

Mitsubishi Motors Corp's President Tetsuro Aikawa attends a news conference to brief about issues of misconduct in fuel economy tests at the Land, Infrastructure, Transport and Tourism Ministry in Tokyo, Japan, April 20, 2016. Reuters

Chairman and Chief Executive Officer Osamu Masuko has already told some affiliated dealers and parts makers of his intention to resign, the Yomiuri daily said. Separately, the Mainichi daily reported President and Chief Operating Officer Tetsuro Aikawa has decided to step down.

Japan's sixth-biggest automaker said on Tuesday it used fuel economy testing methods that did not comply with Japanese regulations for 25 years. It said it would set up an external committee to investigate the matter and report the results in three months. It first flagged the manipulation on four models last Wednesday.

Masuko and Aikawa are expected to resign after the committee reports the results, according to the newspapers.